Routine clinical procedures for tyrosine metabolites in body fluids are badly needed. We have recently developed an extremely sensitive technique for phenolic compounds which takes full advantage of both electrochemistry and high performance liquid chromatography to make measurements on the 0.1 picomole level practical using rather inexpensive apparatus. This approach forms the nucleus of clinical methods for tyrosine and tryptophan metabolites and related molecules in urine, blood, and tissue. The assays under development are specifically designed to maximize the clinically useful information obtainable by inexperienced personnel, while minimizing sample turnaround time. We are confident that data obtained by the improved methods will be more reliable than that presently available. The new assays will eventually be used, with well defined clinical populations, to more completely evaluate the diagnostic and prognostic value of body fluid levels to tumors f the sympathetic nervous system, affective disorders, myocardial infarction, and resistance to physical stress.